BuzzSkito Mosquito & Tick Control Specialists · Published August 22, 2026
As an Amazon Associate, BuzzSkito earns from qualifying purchases. BuzzSkito only points to products we would genuinely use or recommend, at no extra cost to you.
Why the Rain Barrel Became the Problem
Municipal and conservation-authority barrel sales have been running across the GTA for years, and they have worked — there are rain barrels behind an enormous number of Mississauga, Brampton, Oakville and Toronto houses that did not have one a decade ago. What went with them, in a lot of cases, was an open reservoir of warm, still, organically rich water sitting against a south-facing wall.
That is not a marginal breeding site. It is close to the ideal one. Culex pipiens — the species most associated with West Nile virus in Ontario — specifically prefers stagnant water loaded with decaying organic matter, which is precisely what a barrel becomes after two months of roof runoff carries leaf fragments and shingle grit into it. The water is undisturbed, it is shaded from wind, it warms fast, and nothing predatory lives in it.
On a larval inspection, the rain barrel is a stop we make on nearly every property that has one, and it produces more often than the birdbath, the tarp, the wheelbarrow or the plant saucers do. It is also the easiest of all of them to fix permanently, which is the reason this page exists rather than a page telling you to get rid of the barrel. There is no reason to give up the water.
If you want the full inventory of what else on a GTA lot holds water long enough to matter, our guide to hidden mosquito breeding spots in the backyard walks the property corner by corner, and does standing water attract mosquitoes covers how little water it actually takes.
The Mesh Specification That Actually Matters
Almost every guide tells you to use “fine mesh” and stops there, which is unhelpful in a store. Here is the usable version.
18x16 fibreglass window screen — the standard roll sold at Canadian Tire, Home Depot and Rona — is fine enough. Its openings are around a millimetre, and there is no mosquito in Ontario that gets through that. You do not need no-see-um mesh, and you should not use it here.
That last part surprises people, so it is worth stating plainly: finer is not better on a rain barrel. Very fine mesh does two bad things. It clogs with pollen, shingle grit and maple keys within a season, and a clogged screen sheds rainwater over the outside of the barrel instead of into it — which defeats the entire point of owning a barrel and creates a wet zone at the foundation into the bargain. The right screen is the coarsest one that still excludes a mosquito.
Where fibreglass is the wrong choice is anywhere an animal can reach. Squirrels and chipmunks tear fibreglass. At the downspout inlet, and on any opening at ground level, use a 20-mesh stainless screen instead — the openings are comparable, the material is not.
Clamp it, do not drape it. This is the failure we see most often. Screen laid over the top of a barrel and held by the lid ring looks sealed on a still day and lifts on a windy one, and a barrel that is open for six hours in July is a barrel that has been laid in. Stainless hose clamps around the barrel neck, or a purpose-made bungee lid ring, cost almost nothing and end the problem.
The Three Openings Almost Everyone Misses
The lid is rarely how they get in. These are.
1. The overflow port
Every barrel has one, because a full barrel has to put the next 30 mm of rainfall somewhere. On a lot of barrels it is a bare 25 mm hole near the top, or a corrugated hose whose far end lies open on the lawn. Either way it is a doorway, and it is a doorway positioned above the waterline where a female mosquito can walk straight in. Screen the port itself, or fit a hose whose end is screened, or — best — remove the problem entirely with a diverter (below).
2. The linking port
Two or three barrels linked together is a genuinely good upgrade: 400–600 L of capacity means a single summer storm actually fills your watering needs for the week rather than overflowing in ten minutes. But every link is another opening. The failure mode is a hole drilled slightly oversize with a hose pushed through it and no gasket, which leaves a crescent gap you cannot see from above. Use a linking kit with gasketed bulkhead fittings and torque them properly.
3. The downspout inlet
The debris grate moulded into most barrel lids has gaps of several millimetres. It stops leaves. It does not stop insects, and it is the single largest opening on the whole assembly. Line it with stainless screen, or run the downspout into a closed diverter instead.
Why a Downspout Diverter Is the Best Upgrade Here
A top-mounted diverter is a fitting that cuts into the downspout, takes water off sideways into the barrel, and sends the excess back down the pipe once the barrel is full. It costs a fraction of a new barrel and it solves three problems at once.
- The barrel can be fully closed. No open top, no debris grate, no separate overflow hose — the two worst openings simply cease to exist.
- Overflow goes back into the drainage system rather than soaking the ground beside the foundation. That saturated strip along the wall is its own chronic damp zone and does not do the basement any favours either.
- Winterizing is one motion. Most diverters have a winter position or a removable insert, so shutting the system down in October is a two-minute job instead of a disconnection project.
If you are buying a barrel system from scratch this is where the money should go first, ahead of a second barrel and well ahead of a decorative barrel shape.
Bti Dunks: The Backstop, Not the Plan
Bacillus thuringiensis israelensis is a soil bacterium that mosquito larvae eat and die from. It does nothing to people, pets, fish, frogs, birds or bees; its activity is confined to the larvae of mosquitoes, black flies, fungus gnats and their close relatives, which is why it is the standard tool for water you cannot drain. One dunk treats roughly 100 square feet of surface for about 30 days — vastly more surface than any residential barrel has — so one dunk per barrel, replaced on the first of the month from May through September, is the whole protocol. Our mosquito dunks guide for Canada covers brands, PCP registration and where they are stocked, and Mosquito Bits vs Dunks explains when the granules are the better format.
Two honest caveats. First, a dunk is a backstop for the screen you did not clamp properly, not a replacement for screening — it does nothing about the leaf sludge that accumulates in an open barrel, and sludge is what makes the water attractive in the first place. Second, dunks only kill what is in your barrel. Adults arriving from a neighbour’s untreated barrel or a ravine two streets over are unaffected, which is the ceiling on every larval-control measure.
If you want to know whether the barrel is already producing, look at the surface: mosquito larvae hang just under it and dart downward when you shade them with your hand. Our page on identifying mosquito larvae shows what wrigglers and tumblers look like versus the harmless things people mistake for them.
Sizing, Stands and the Part About 200 Kilograms
A standard Canadian rain barrel holds 190–220 L (50–58 US gallons). One millimetre of rain on 10 square metres of roof yields about 10 L, so a modest roof section fills a barrel in a single ordinary summer storm. That is the argument for linking barrels rather than buying a bigger one: capacity you can actually use, and a spare barrel is cheaper than an oversized custom tank.
The stand matters more than it looks. The spigot sits near the bottom of the barrel, so gravity flow depends entirely on how high the barrel sits. At ground level you get a dribble that will not run a soaker hose; at 300–450 mm (12–18 in) you get usable pressure for a watering can or a short hose run.
The safety note that belongs on every rain barrel page and appears on almost none: a full 200 L barrel weighs about 200 kg. That load goes on whatever you set it on. Concrete blocks on level, compacted ground are fine — set them cores-up rather than on their sides, which is the orientation they are rated to carry. Scrap lumber, a stack of patio slabs on soft soil, or a deck railing are not. A wooden deck is the case to think hardest about: 200 kg concentrated on a barrel-sized footprint is several times the uniform load a typical residential deck is designed for, so put the barrel on the ground or a pad if you possibly can, and if it has to go on the deck, site it directly over a beam or a post rather than mid-span — and ask a contractor if the span is long or the deck is old.
When the Cheap Fix Is the Right Fix
A page like this has an obvious commercial temptation, so here is the honest version.
If you already own a barrel with a sound lid, do not buy a new one. A roll of fibreglass screen, a handful of stainless hose clamps and a pack of Bti dunks will mosquito-proof it for well under $50, and the result is functionally identical to a $250 system. Screen the overflow, line the inlet grate, clamp the lid, drop a dunk in. Done in twenty minutes.
Add the diverter next, at around $30–$60, because it eliminates openings rather than covering them and it fixes the foundation-soaking problem too. That is the highest-value single purchase on this page.
The full $120–$400 build is for a specific person: someone starting from nothing, or scaling to two or three linked barrels on a stand with a proper brass spigot because they actually irrigate a large garden from it. If that is you, buy it as a system so the fittings match. If it is not you, the cheap retrofit is not a compromise — it is the correct answer, and a barrel with a $12 screen on it breeds exactly as few mosquitoes as a barrel with a $300 one.
What is never worth it: a decorative barrel with a large open grate top chosen on looks. Those are the barrels we find producing larvae, every season, and no amount of after-market screening makes an open grate as tight as a sealed lid.
Winter: The Ontario Half of the Job
Rain barrels fail in Canada mostly in February, and the consequences show up in June.
Drain the barrel completely before the first hard freeze — late October in most of the GTA, earlier north of Highway 7 and in Caledon or King City. Leave the spigot open so any residual water has somewhere to go as it expands. Disconnect the diverter or switch it to its winter position, and either invert the barrel or store it in the garage. Water left in a barrel expands as it freezes and splits the wall or, more commonly, cracks the plastic spigot fitting — and a cracked fitting is an unscreened opening you will not notice until something is breeding behind it.
The spring restart matters just as much. Rinse the winter sludge out before refilling. That layer of decomposed leaf matter on the bottom is the food supply, and a barrel started clean in April is a barrel that stays uninteresting all season. It is worth doing in the same week you check the rest of the yard — see the mistakes Ontario homeowners make for the rest of that spring list.
Where to Buy the Parts in Canada
Barrels themselves are widely stocked seasonally — Canadian Tire, Home Depot, Rona and Lowe’s all carry them from roughly April through July, and municipal or conservation-authority truckload sales across the GTA are usually the cheapest route if the timing lines up. Screen rolls, hose clamps and downspout hardware are year-round stock at all four.
Where amazon.ca earns its place is the awkward middle: gasketed linking kits, brass bulkhead spigot assemblies, screened overflow kits and barrel stands are the items that are either seasonal or simply not carried in a given store, and they are the ones you need when a barrel already in your yard needs a specific part in August. Bti dunks are stocked everywhere in spring and thin out badly by mid-July, which is exactly when you discover you need them.
The Bottom Line
A rain barrel is not a mosquito problem. An unscreened rain barrel is. Screen every opening into the water with 18x16 fibreglass mesh — clamped, not draped — pay particular attention to the overflow port, the linking port and the downspout inlet, and drop one Bti dunk in per barrel per month from May to September. If you are building the system rather than fixing one, put the money into a top-mounted diverter before anything else, because it removes openings rather than covering them. Then drain it before the freeze, rinse it in April, and forget about it — which is the whole point.
Frequently Asked Questions
Do rain barrels breed mosquitoes?
An unscreened rain barrel is one of the most productive mosquito breeding sites a suburban Canadian yard can contain. It holds warm, still, organically rich water that nothing disturbs, which is exactly what Culex pipiens — the mosquito species most associated with West Nile virus in Ontario — looks for when laying an egg raft. A properly sealed barrel breeds nothing at all. The difference is not the barrel; it is whether every opening into the water is screened, including the two most people forget: the overflow port and the downspout inlet.
What size mesh keeps mosquitoes out of a rain barrel?
Standard fibreglass window screen — the 18x16 mesh sold by the roll at every Canadian hardware store, with openings around 1 mm — is fine enough to stop every mosquito species in Ontario. You do not need no-see-um mesh, and finer is not automatically better: very fine mesh clogs with pollen, shingle grit and maple keys, and a clogged screen sheds rainwater over the side of the barrel instead of into it. Use 18x16 fibreglass or a 20-mesh stainless equivalent, and clamp it down rather than draping it, because wind lifts a loose screen and a lifted screen is an open barrel.
Where do mosquitoes actually get into a screened rain barrel?
The lid is rarely the problem. On larval inspections the three openings that let mosquitoes in are: the overflow port, which is often a bare 25 mm hole or a hose with an unscreened open end; the linking port between two barrels in a linked pair, where the bulkhead fitting has no gasket or has been drilled oversize; and the downspout inlet, where a debris grate with 5 mm gaps is doing nothing to stop an insect. Screen or plug all three. A mosquito needs an opening the size of a pen tip, and she will find it.
Do mosquito dunks work in a rain barrel?
Yes, and they are the right backstop even on a properly screened barrel. Bti (Bacillus thuringiensis israelensis) kills mosquito larvae and does nothing to people, pets, fish, birds or pollinators. One dunk treats roughly 100 square feet of water surface for about 30 days, which is far more surface than any residential barrel has, so one dunk per barrel replaced monthly from May through September covers it. Use Bti as insurance against the screen you did not clamp properly — not as a substitute for screening, because a dunk does not stop the barrel filling with leaf sludge.
Is water from a rain barrel safe to use on a vegetable garden?
Use it on lawns, shrubs and ornamentals freely. For food crops, the usual Canadian guidance is to keep roof runoff off the edible parts of the plant — water the soil, not the leaves, and avoid it entirely on low leafy greens you eat raw. That caution is about the roof, not about Bti: asphalt shingles shed grit, and roofs collect bird droppings. Bti dunks themselves do not change the answer either way; a Bti-treated barrel is no less suitable for garden use than an untreated one.
Does a downspout diverter stop mosquitoes?
Indirectly, and it is the single best structural upgrade on this list. A top-mounted diverter takes water off the downspout into a closed barrel and returns the excess back down the pipe once the barrel is full, which means the barrel never needs an open top or a separate overflow hose running across the lawn. Fewer openings means fewer ways in. The second benefit is that overflow goes back into the drainage system instead of soaking the ground at the foundation, which is itself a chronic wet zone in a GTA backyard.
When should I drain and disconnect a rain barrel in Ontario?
Before the first hard freeze — late October in most of the GTA, earlier north of Highway 7. Drain the barrel completely, leave the spigot open, disconnect the diverter and either invert the barrel or store it. Water left in a barrel over an Ontario winter expands as it freezes and splits the wall or cracks the spigot fitting, and a cracked fitting is an unscreened opening next May. The spring reconnection matters just as much: rinse out the winter sludge before you refill, because that layer of decomposed leaf matter is what feeds larvae.
How fast can mosquitoes breed in a rain barrel?
In GTA July heat, a Culex egg raft laid on a Monday can be producing flying adults inside seven to ten days. That number is why the common advice to "empty your barrel weekly" is not a safety margin — it is the exact edge of the breeding cycle, and one missed weekend puts you over it. Sealing the water off is a permanent fix that does not depend on you remembering. It is also the reason a barrel is worth fixing at all rather than removing: a screened barrel is a non-issue, and there is no reason to give up the water.
